Transmission Electron Microscopy (TEM) is a method of analyzing extremely small features of a material, typically 0.5 nm to about 100 nm. TEM generally monitors electrons as they are transmitted through a thin material. As such, thinner materials can provide better TEM images than thicker materials. This is because electrons can transmit more easily through the thin material.
TEM is often used in the semiconductor industry. For example, TEM can be used to determine whether the features formed on a device conform to design specifications. For proper TEM analysis, a region of the material having a feature of interest should be made thinner than the feature of interest. This is because when the material thickness exceeds the feature size, the data obtained by TEM may be misinterpreted, distorted, or may show the superposition of multiple features. All of these issues can result in an unacceptable TEM analysis. Thus, there is a need to thin the material as much as possible. However, as the critical dimensions in the semiconductor industry continue to scale down, it is becoming increasingly more difficult to sufficiently thin materials for TEM.
Conventional TEM sample preparation removes a thin portion of material from a bulk material. This is typically done using FIB. The FIB uses a beam of ions, such as a beam of gallium ions, to cut the thin material from the bulk. Currently, an experienced FIB user is able to cut a sample to have a minimum thickness of 500 Å without causing too much amorphization of the sample. However, various features on state of the art semiconductor devices can be smaller than this minimum thickness, and, as stated above, this can result in analysis errors.
Some problems that limit the preparation of thinner materials using FIB include poor mechanical stability of the material and poor thermal transport during FIB and amorphization of the surface. As such, it has not been possible to produce a material thinned to a sufficient degree so as to allow accurate analysis.
Accordingly, the present invention solves these and other problems of the prior art when forming thinned material that can provide accurate TEM analysis.